Showing papers on "Redundancy (engineering) published in 1978"

Reliability Issues in Computing System Design

Abstract: This paper surveys the various problems involved in achieving very high rehability from complex computing systems, and discusses the relatmnship between system structurmg techniques and techniques of fault tolerance. Topics covered mclude: 1) protective redundancy in hardware and software; 2) the use of atomic actmns to structure the activity of a system to limit mformatmn flow; 3) error detection techniques; 4) strategies for locating and dealmg with faults and for assessing the damage they have caused; and 5) forward and backward error recovery techmques, based on the concepts of recovery line, commitment, exceptmn, and compensation. The ideas described relate to techmques used to date in systems mtended for environments in whmh high reliability is demanded Three specific systems the JPL-STAR, the Bell Laboratories ESS No. 1A processor, and the PLURIBUS are described m some detail and compared.

Instrument Fault Detection

Abstract: The dedicated observer scheme (DOS) for detecting incipient instrument faults by functional redundancy is applied to a simulation of the lateral axis control system of a hydrofoil boat. Observer designs and detection logic are found for which 14 separate instrument faults are detected without false alarms. The scheme is shown to be robust with respect to variations in two significant physical parameters.

Multiple word/bit line redundancy for semiconductor memories

Abstract: Multiple word/bit line redundancy techniques at the chip level are shown to be powerful enough to obtain good yields for chips with much higher rates of faults/chip than without redundancy. This is possible because, in many instances, chips which are rejected as being bad still have a high percentage of usable bits on them. The redundancy techniques described consist of putting spare decoders and spare word and bit lines on a chip in order to be able to replace defective lines of the chip with good lines while still maintaining the same address. Based on a first-pass design of a 16K chip, a significant improvement in the number of usable bits per wafer appears possible. The leverage for improvement is shown to be strongly dependent upon the type of cell, the layout, and the technology used.

Power-system state estimation using linear programming

Abstract: The problem of estimating the state variables from measurements in an electric-power system is considered. The conventional linearised least-squares solution is shown to be ineffective in the presence of gross measurement errors. Reformulating the problem as a linear program leads to a state estimator that combines the advantages of noise filtering and bad-data elimination, and may be implemented straightforwardly by application of the simplex method. The solution of various examples based on three test networks confirms the advantages of the method especially where the data are corrupted by a number of gross errors. Depending on the degree of redundancy in the measurement set, the computational requirements of the method are comparable with conventional least-squares solution. For real-time power-system monitoring and control where process variables have unknown statistics, the linear-programming method is believed to be more efficient than conventional algorithms.

Fault Detection Capabilities of Alternating Logic

Abstract: This paper details the fault detection capability of a design technique named "alternating logic design." The technique achieves its fault detection capability by utilizing a redundancy in time instead of the conventional redundancy in space and is based on the successive execution of a required function and its dual. In combinational networks the method involves the utilization of a self-dual fumction to represent the required function and the realization of the self dual function in a network with structral properties which are sufficient to guarantee the detection of all single faults. One network structure with sufficient structral properties to detect all single stuck-line faults is the standard AND/OR or OR/AND two-level network [1]. However, other more general combinational logic structures also possess sufficient structural properties. Necessary and sufficient structural properties for any alternating network to be capable of detecting all single faults are derived.

Synchronization and Matching in Redundant Systems

Abstract: Most of the published work on massive redundancy makes one crucial assumption: the redundant modules are synchronized. There are three ways of achieving synchronization in redundant systems-independent accurate clocks, a common external reference, and mutual feedback. The use of a common external reference is currently the most widely used technique, but suffers from vulnerability to common-point failures. We introduce a novel mutual feedback technique, called "synchronization voting," that does not have this drawback. A practical application of synchronization voting is described in the appendix—a fault-tolerant crystal-controlled clock.

A Note on Heuristic Methods in Optimal System Reliability

Abstract: Many optimization techniques have been used to solve redundancy allocation problems, most of which result in noninteger solutions. A few, including dynamic programming and integer programming, as well as a host of heuristic methods give integer solutions. This note critically reviews six promising heuristic approaches. The advantages and disadvantages of each of the approaches are discussed. An extended approach is presented which incorporates some of the ideas of the previous methods for solving a general non series-parallel system. The extended approach appears to be quite efficient and is general. The simplicity and efficiency of the approach will lend itself to solving large practical problems.

An Improved Algorithm for Reliability Optimization

Abstract: This paper proposes a modification of the Aggarwal et al. algorithm for reliability optimization by introducing a new heuristic criterion for selecting the subsystem where redundancy is to be added. This criterion accounts for the relative decrement in unreliability versus the largest of the relative increments in resources. The method applies to multiple separable constraint problems (which need not be linear) and to systems which may be complex or series. The method is simple, fast, and easily programmed. The results are compared with those of the Aggarwal et al. algorithm and are better in many problems.

Reliable Computing Systems

Abstract: The paper presents an analysis of the various problems involved in achieving very high reliability from complex computing systems, and discusses the relationship between system structuring techniques and techniques of fault tolerance. Topics covered include (i) differing types of reliability requirement, (ii) forms of protective redundancy in hardware and software systems, (iii) methods of structuring the activity of a system, using atomic actions, so as to limit information flow, (iv) error detection techniques, (v) strategies for locating and dealing with faults, and for assessing the damage they have caused, and (vi) forward and backward error recovery techniques, based on the concepts of recovery line, commitment, exception and compensation. A set of appendices provide summary descriptions and analyses of a number of computing systems that have been specifically designed with the aim of achieving very high reliability.

Sift-Out Modular Redundancy

Abstract: A fault-tolerance technique for digital systems, Sift-Out Modular Redundancy, is proposed and designed. An appropriate number of identical channels are provided for each module. The number of channels depend upon the particular application, and all channels are active as long as they are fault-free. Upon the failure of a channel, its contribution to the module output ceases. The configuration tolerates up to L − 2 channel failures, if L is the initial number of channels. Sift-out redundancy is easy to implement, and shows several advantages when compared to existing redundancy techniques.

Redundancy CAM using word line from memory

Abstract: A redundancy programming circuit employing a two EPROM cell CAM for storing programmed states of redundant elements. The CAMs are disposed aside a memory array and word lines of the array are extended to the CAMs for programming the CAMs. Two word lines are coupled to each EPROM cell so that programming can still be achieved in the event one of the lines is defective.

On reliable control system designs with and without feedback reconfigurations

Abstract: This paper contains an overview of a theoretical framework for the design of reliable multivariable control systems, with special emphasis on actuator failures and necessary actuator redundancy levels. Using a linear model of the system, with Markovian failure probabilities and quadratic performance index, an optimal stochastic control problem is posed and solved. The solution requires the iteration of a set of highly coupled Riccati-like matrix difference equations; if these converge one has a reliable design; if they diverge, the design is unreliable, and the system design cannot be stabilized. In addition, it is shown that the existence of a stabilizing constant feedback gain and the reliability of its implementation is equivalent to the convergence properties of a set of coupled Riccati-like matrix difference equations. In summary, these results can be used for off-line studies relating the open loop dynamics, required performance, actuator mean time to failure, and functional or identical actuator redundancy, with and without feedback gain reconfiguration strategies.

The role of spatial redundancy in grapheme recognition: perception or inference?

Abstract: The question under investigation is whether spatial redundancy operates by restricting the number of valid alternatives at each serial position or whether it serves a perceptual function by keeping visually confusable graphemes from appearing in the same array and/or maximizing the distance between such graphemes when they do occur in the same array. The first experiment used the same-different task to establish a confusion matrix for 12 non-linguistic symbols. The spatial relation between the members of two pairs of confusable symbols was manipulated in a second experiment, which had subjects look for the presence or absence of a predetermined target symbol in single six-symbol linear arrays. Facilitation was found to be dependent upon the perceptual consequences of serial position constraint rather than upon the constraint per se. The constraint was most effective when it served to prevent members of visually confusable pairs from occurring in the same array. Since spatial redundancy may operate at the feature extraction stage by minimizing competition for the same sets of feature detectors and since words are likely to be high in spatial redundancy, the possibility is raised that part of the word superiority effect may be due to visual factors rather than to linguistic context.

Computing relative redundancy to measure grammatical constraint in speech recognition tasks

Abstract: In this paper we present new and computationally efficient algorithms for computing some statistical properties of finite languages. In particular, the relative redundancy which measures grammatical constraint, is computed for several speech recognition task languages which have appeared in the literature.

An investigation of the perceptual basis of redundancy gain and orthogonal interference for integral dimensions.

Abstract: Redundancy gain and orthogonal interference for height and width were demonstrated in two experiments using a relative coding task with number of intertrial repetitions controlled. Orthogonal interference was shown to be perceptually based rather than simply an intertrial repetitions effect as suggested by Felfoldy (1974). These results from a relative coding task were discussed in terms of the previous multidimensional processing literature. It was concluded that Lockhead’s (1972t model has been applied too generally. An alternative model (a parallel, dimensional analysis stage followed by a stage in which dimensional information is integrated) was suggested.

Analysis of a Dynamic Redundant System

Abstract: This paper considers a Safeguard which upon demand should initiate some action within a short time. A form of dynamic redundancy is introduced and the reliability of a Safeguard is analysed on the basis of two computer algorithms. Both fail-to-safe and fail-to-danger probabilities are considered. The advantage of this form of redundancy over conventional r-out-of-n:G systems is discussed, and the algorithms are illustrated by way of examples. Comparative results for various redundant configurations are given.

The Evolutionary Significance of Redundancy and Variability in Phenotypic-Induction Mechanisms of Pierid Butterflies (Lepidoptera)

Abstract: One of the major discoveries in the study of seasonal polyphenistn in butterflies was the role of larval photoperiodic exposure (Danilevskii, 1948). Following this discovery, experiments on two Pierid species Colias eurytheme Bdv. (Watt, 1969; Hoffrnan, 1974)and Pieris protodice Bdv. & LeC. (Shapiro, 1968) appeared to establish that temperature played no role in the seasonal polyphenisms of that family. This was clearly not the case in at least one Nytnphalid, Araschnia levana (L.): Siiffert (1924) had shown a tetnperature effect, and later work by Danilevskii (1948), Mfiller (1955, 1956, 1960), Reinhardt (1969, 1971), and Mtiller and Reinhardt (1969) showed that photoperiod and temperature interact in a characteristic way. Long-day larvae or young pupae, nortnally destined to produce the summer fortn prorsa, if experimentally cooled will produce either the winter fortn levana or an intertnediate fortn (porima). Short-day larvae give rise to diapause pupae which always give levana, regardless of temperature. Thus photoperiod, acting on 4thand 5th-instar larvae, can irreversibly detertnine the vernal phenotype, but not the estival one, which can be overridden by temperature acting on the young pupa. Shapiro (1977) established that pupal diapause and adult phenotype, nornally tightly coupled in the Pieris napi (L.) group of Pieridae, could be decoupled in P. n. venosa Scudder. In napi generally, diapausing pupae give rise to vernal phenotypes and nondiapausing ones to estival phenotypes. Populations consist of a tnixture of obligate diapausers, apparently detertnined genetically, and facultative ones responsive to daylength. In some but not all populations, inducing photoperiods can be overridden by high

Reduced redundancy facsimile transmission installation

Abstract: The invention relates to a reduced redundancy facsimile transmission installation which includes at the transmission end means which form run length words from the binary data analysis of a document. In accordance with the invention, at the transmission end, an array of combinatorial logic circuits (26), preferably of the PLA type, is programmed to transcode run length words into other words, using a truncated Huffman code and, at the receiving end, arrays which are also preferably of the PLA type provide inverse transcoding. Application: facsimile transmission.

Automatic damper means and controls therefor

Abstract: An automatic damper means and controls, which provide an exceedingly safe automatic damper for the exhaust duct-work of an associated gas furnace or the like, by automatic control of the damper, and automatic control of the gas supply, with redundancy features for providing exceedingly safe operation.

Programming Distributed Systems

Abstract: For a number of technical and economic reasons, distributed computing is increasing rapidly in importance. The main technical considerations are the increased performance of small machines and of communications systems relative to that of giant computers and the opportunity for greater system reliability through redundancy. The economic considerations include all of the technical ones plus additional aspects including the geographic dispersal of needs and the organizational advantages of more specialized facilities (cf. Bank of America article in Datamation [1976]). The Computer Science Department of the University of Rochester has, from its inception in 1974, directed much of its research effort toward a better understanding of distributed computing.

A Moment Approach to Evaluation and Optimization of Complex System Reliability

Abstract: A moment approach to evaluating reliability of complex systems is described. The advantages of this type of model have been discussed in relation to models based simply on probability of failure. The main difficulty of a moment approach is the evaluation of first and second moments of the system failure-time distribution. A proposed theorem considerably alleviates this difficulty. In order to facilitate applying this theorem, approximate expressions for the mean and variance of parallel systems are suggested. The problem of system optimization is then discussed and the technique is illustrated with a bridge network. If the system s-expected life remains unchanged when redundancy is added, the variance of system life always decreases.

A survey and methodology of reconfigurable multi-module systems

Abstract: In multi-module and multi-processor systems, system performance can be greatly enhanced by the use of reconfiguration. In this paper we attempt to categorize and present standard definitions for the many different types of reconfigurable systems. Illustrations from the literature for each category are presented.